In general, the motion of jointed mechanical devices, such as robotic hand prosthetic devices, can be controlled with control signals and/or sensors monitoring the motors within the jointed mechanical device. However, fine motor control of such devices is typically difficult to achieve, as the amount of feedback sensory information available in natural limbs and appendages greatly exceeds the amount of feedback information typically available in conventional jointed mechanical devices. Although some jointed mechanical devices have been constructed to include additional feedback sensors, the additional costs, complexity, and weight associated with such feedback sensor systems are generally impractical.
Additionally, the number of signals available for controlling such devices is fairly limited, resulting in only a few types of inputs being available for a relatively large number of components. For example, in some types of robotic prosthetic devices, a measurement of the electric potential generated by the muscles in a residual limb, commonly referred to as an electromyogram (EMG) signal, is used to control the movements of the prosthesis. In such devices, EMG signals can be used to command the forward and/or reverse velocity of one or more electric motors configured to actuate the prosthesis. One common type of robotic prosthetic device using EMG signals is a myoelectric hand and/or arm prosthetic device.
Hand and/or myoelectric prosthetic devices typically operate based on EMG signals generated by the muscles of the residual forearm or upper arm. However, a residual limb typically only produces a few usable EMG signals. Consequently, even though such prosthetic devices can be designed to be anthropomorphic to provide a visually pleasing prosthesis, the limited number of EMG signals generally results in limited utility. In the case of conventional myoelectric hand prostheses, only a sophisticated claw is generally provided. That is, these prosthetic devices are generally designed to provide a “pinch-type” operation, permitting the user to grasp an object but little else. Although, the ability to grasp and hold objects can be a significant improvement in the lifestyle of a hand and/or arm amputee, the utility of such devices is limited. Although more sophisticated designs are available, the additional costs, complexity, and weight associated with such devices are generally impractical.